Hydatid cyst, with an atypical appearance on CT
Computed tomography (CT) of the liver was obtained before and
after the administration of 120 mL of nonionic contrast (Omnipaque
350, GE Healthcare, Princeton, NJ) on a Sensation 16 scanner
(Siemens Medical Solutions, Malvern, PA) using 0.75-mm collimation,
120 KVp, 300mAs, 0.75 slice thickness with reconstruction of data
every 0.5 mm. The axial images showed a well-defined, avascular
3-cm ovoid lesion in the left lobe (Figure 1). The lesion measured
51 HU before the administration of contrast, with no evidence of
enhancement on either thearterial- or venous-phase images. The
lesion was poorly visualized on both noncontrast and arterial-phase
contrast-enhanced CT but was clearly seen as a well-defined,
low-density mass on venous-phase imaging.
Based on the CT findings, the possibility of an atypical hepatic
adenoma or focal nodular hyperplasia was initially considered but
was considered unlikely. In light of the recent history of weight
loss, there was a concern for neoplasm or abscess, and so a biopsy
was performed. Under ultrasound guidance, 2 passes with a 22-gauge
Chiba needle were performed in the lesion. Evaluation of the
aspirated material revealed the presence of echinococcal hooklets,
yielding a final diagnosis of hydatid cyst (Figure 2). The patient
was placed on albendazole therapy and referred to a
gastrointestinal parasitologist for further treatment.
After the biopsy, it was discovered that the patient had taken 2
trips to Mexico within the past 2 years and that her symptoms had
begun just after her first trip.
Hepatic cystic echinococcosis is caused by infection with the
metacestode stage of the tapeworm Echinococcosis
granulosus. The disease remains endemic in many parts of the
world, including the Mediterranean, the Middle East, and parts of
South America. Initial infection is always asymptomatic, and
subsequent clinical manifestations depend on cyst size and the site
of infection. Although hydatid cysts may be found in almost any
area of the body, the liver is the most frequent site of
involvement, with the majority of cysts affecting the right lobe.
In a study of 368 patients with hydatid disease, nearly 75% had
liver involvement and nearly half of those had cysts solely in the
liver.1Hepatic cysts can remain asymptomatic for years,
but growth and rupture of hydatid cysts can have serious sequelae.
Cyst growth can produce a mass effect that restricts bile orvenous
drainage through the portal system, resulting in cholestasis or
portal hypertension. Secondary bacterial infection may lead to the
development of liver abscesses. Rupture of cyst contents into the
biliary tree can cause cholangitis, obstructive jaundice, or
The differential diagnosis of a solitary hepatic cystic mass is
broad and includes simple (bile duct) cyst, benign adenoma, focal
nodular hyperplasia, metastatic lesion, biliary cystadenoma or
cystadenocarcinoma, primary hepatoma, pyogenic or amebic abscess,
and echinococcal cyst. Imaging findings on CT can help to narrow
Simple cysts result from congenital defects in bile-duct
formation.3 Radiographically, they are well-defined,
measure water density, and do not exhibit enhancement after the
administration of intravenous contrast. This lesion did not measure
water density and did not exhibit enhancement (either early or
Hepatic adenomas and focal nodular hyperplasia are usually
hypervascular and, unlike the lesion in this case, usually enhance,
especially during the arterial phase. The possibility of atypical
avascular adenoma remained on the differential until the time of
biopsy, as did focal nodular hyperplasia. Primary hepatoma and
metastasis were also included in the differential diagnosis,
although in sequential imaging these generally enhance to a greater
degree than as seen in this case. Cystadenomas appear as
low-attenuation intrahepatic masses on CT as well. They are
typically more cystic in nature than hydatid cysts, with thick
nodular walls and septations. Pyogenic abscesses are variable in
appearance radiographically and can often be confused with amebic
abscesses. However, both can generally be distinguished from
hydatid cyst (and from each other) by correlation with the clinical
picture and laboratory data.4
An echinococcal cyst is most often seen radiographically as a
well-defined area of low attenuation on CT, often with several
classic diagnostic findings. These include focal or segmental cyst
wall thickening, crescentic calcification of cyst borders, and the
presence of daughter cysts.5 None of these CT findings
were apparent in this case.
Classically, the diagnostic imaging method of choice for
assessing cystic lesions of the liver has been ultrasound, as it is
noninvasive, accessible, and sensitive.6 However, as the
use of CT as a primary imaging modality continues to rise, and as
CT has become a preferred modality in the investigation of liver
lesions, it is important to consider hydatid cyst in the
differential diagnosis when presented with unusual cystic lesions
in the liver, regardless of whether classic CT features are
present. This case illustrates that a detailed clinical history is
essential in narrowing down a differential diagnosis-especially
when imaging findings are nonspecific.
Hydatid disease remains an endemic problem in many parts of the
world. Despite attempts to identify imaging findings that
distinguish hepatic echinococcal cysts from other hepatic cystic
lesions, echinococcosis is still a challenging disease to diagnose
radiographically. This case of hydatid cyst in the liver with
atypical CT findings demonstrates the importance of a broad
differential diagnosis that includes hydatid cyst when
investigating any unusual hepatic cystic lesions.
- Polat P, Kantarci M, Alper F, et al. Hydatid disease from head
to toe. RadioGraphics. 2003;23:475-494; quiz 536-537.
- Parwani AV, Burroughs FH, Ali SZ. Echinococcal cyst of the
liver. Diagn Cytopathol. 2004;31:111-112.
- Cowles RA, Mulholland MW. Solitary hepatic cysts. J Am Coll
Surg. 2000;191:311-321. Comment in: J Am Coll Surg.
- Murphy BJ, Casillas J, Ros PR, et al. The CT appearance of
cystic masses of the liver. RadioGraphics.
- Haddad MC, Birjawi GA, Khouzami RA, et al. Unilocular hepatic
echinococcal cysts: Sonography and computed tomography findings.
Clin Radiol. 2001;56:746-750.
- Sayek I, Onat D. Diagnosis and treatment of uncomplicated
hydatid cyst of the liver. World J Surg.